This work is related to the efforts of the Boston Retinal Implant Project to develop a sub-retinal prosthesis to restore vision to the blind. We present new high density packaging advancements for the Boston prosthesis, and bonding processes for the exterior of the packages.

Methods

Co-fired ceramic structures with signal feedthroughs formed from a platinum-rhodium alloy were fabricated to mate with hermetic packages for the retinal implant; feedthrough discs were gold brazed to the miniature titanium housings. In subsequent assembly steps, flexible electrode arrays with electroplated gold contact pads were joined to the feedthrough assemblies by thermo-compression bonding. A custom fixture for making temporary contact to the bonded prostheses for testing purposes was designed and built, which allowed the bonded devices to be wirelessly tested before affixing the protective headers.

Results

Tests of the retinal implant assemblies' quality were performed by helium leak testing and bond pull tests. In the Figures, the co-fired ceramic discs and the bonded prosthesis assemblies are shown. When thermo-compression bonds to the prosthesis' iridium oxide electrode arrays were performed at 150 degrees C had an average shear strength of more than 50 grams force, indicating good quality bonding. Room temperature bonds were markedly weaker. Helium leak rates better than 1.0x10E-09 standard cc He / second were measured. The completed assemblies were extensively tested wirelessly in vitro and can monitor individual electrode voltage waveforms via on-chip analog to digital converters.

Conclusions

Improved feedthrough fabrication and bonding methods to miniature implantable titanium retinal prosthesis assemblies have been demonstrated, and completed retinal implants having 256+ channels were successfully tested wirelessly. These results pave the way for clinical testing of the Boston retinal prosthesis in the near future.